Blades for wind turbine systems were traditionally made of several fiber-reinforced resin containing components. Commonly, blades are casted in one piece or in several pieces, for example two shells, which are then glued to each other. The dominant processing method of producing the resin containing components such as the blades is vacuum resin infusion. An alternative processing method is prepreg molding with woven or unidirectional glass fabrics which already contain the resin as the matrix material.
In order to withstand large and repeated loads, the wind turbine blades were conventionally made from thermoset resins having good mechanical properties. Therefore, typical resin containing components were laminates composed of several reinforced resin layers overlaying each other and building up the finished blade structure. Generally, the blade materials were selected to provide a high rigidity and resistance to torsion and fatigue to the blades. Because of the mechanical performance of such blades, epoxy resins were typically used, especially, if longer blades of more than 40 or 50 m were manufactured. Similar techniques and resin materials for composite structures were applied in the automotive industry for example.
The amount of reinforced resin material used in such thermoset elements make the resultant parts heavier than corresponding non-reinforced parts, wherein the amount of reinforcement used generally depends on the mechanical requirements. In the patent application US 2002/01787702 A1, composite parts for automotive applications have been proposed which are made of a combination of a thermoplastic first layer and a second thermoset layer. The first layer made of a thermoplastic material provides a good surface finish and reduces overall part weight, while the second layer made of a thermoset resin provides a good strength and rigidity to the composite part. The thermoplastic layer and the thermoset layer are bonded to each other by the use of an adhesion site activated by a component of the unreacted thermoset resin that acts on a component of the thermoplastic resin or by a mechanical penetration of a thin, porous layer by the two resins. Styrene groups are used as such active sites.
The incorporation of some thermoplastic elements into a composite structure as has been described in the field of automotive applications was also considered in the field of wind turbine blades. These considerations were made either for enhancing processing capabilities or for achieving an effect of the element in the use of a laminate.
In wind turbine blade applications, however, it was investigated that the resulting mechanical properties of the laminate material comprising thermoplastic and thermoset resins were affected to some extent, most often negatively. This was caused mainly from inferior material properties of the thermoplastic or inferior interface properties between the thermoplastic and the thermoset resin layers. Therefore, if such composites were applied, the amount of thermoplastic materials in the composite structures was reduced as much as possible.